Problem with non-additive measure

I have to create a non-additive measure in a cube, but selecting 'None' as aggregate function gives me empty cells when I browse the cube.

To illustrate what I'm looking for:
I calculate revenue in a measure and the non-additive measure should retrieve the target value that had been defined for a specific customer and category combination. Creating a calculated member for an average sum(target)/count(target) doesn't work as it averages over all categories and it needs to retrieve a unique target value for each customer / category combination. The table is as follows: